Synthesis, crystal structures and properties of three sodium coordination polymers based on bridging polyoxometalate ligands

Abstract

The syntheses, crystal structures, spectral characterization, electrochemical, photoredox properties and biological studies of three sodium coordination polymers viz. (ImH) sub(4)[(Mu sub(2-)HMo sub(7)O sub(24))Na(H sub(2)O) sub(8)].7H sub(2)O 1 (Im = Imidazole), [(TEAH)Na sub(5)(H sub(2)O)12(Mu sub(5-)Mo sub(7)O sub(24))] sub(2) (TEA=triethanolamine) and [Na sub(2)(PyrH) sub(2)(Mu sub(2-)Mo sub(8)O sub(26))(H sub(2)O)7].8H sub(2)O 3 (Pyr = pyrazole) are reported. The unique Na atom in 1 exhibits ten coordination unlike hexa coordination observed in 2 and 3. The Mu sub(2-) bridging heptamolybdate (or octamolybdate) anion in 1 (or 3) links the sodium cations into an infinite chain resulting in a one-dimensional coordination polymer. In 2, the heptamolybdate anion exhibits an unprecedented Mu sub(5-) nonadentate binding resulting in a three- dimensional (3D) structure. Compounds 1-3 exhibit characteristic Raman bands. Solar irradiation of 2 results in photodimerization, which is further supported by electrochemical studies. Compounds 1-3 exhibit antibacterial activity, with 3 being the most effective against S. Pyogenes, followed by P. aeruginosa, S.typhi and S. aureus. Compound 3 exhibits excellent antidiabetic and anti-inflammatory properties. A comparative study of the binding modes of several heptamolybdates and octamolybdates based compounds is presented.